Pasteurisation of fine cut tobacco

ABSTRACT

There is provided a method of making a product containing pasteurised fme cut tobacco for combustible use. The method comprises arranging fme cut tobacco (1) comprising elongate strips of tobacco having a cut width of less than 0.5 mm and a moisture content of at least 18 percent by weight, and heating the fme cut tobacco (1) such that the tobacco is pasteurised. Further, there is provided a product containing pasteurised fme cut tobacco (1) for combustible use. The product comprises a closed package (2); and pasteurised fme cut tobacco (1) within the closed package (2), the pasteurised fme cut tobacco (1) having a cut width of less than 0.5 mm and a moisture content of at least 18 percent by weight, and a colony forming unit (CFU) value of less than 2 log lo colony forming units per gram.

The present invention relates to a product containing pasteurised fine cut tobacco, and a method for making a product containing pasteurised fine cut tobacco.

Various forms of tobacco exist for various forms of smoking and smokeless articles, and the properties of each form of tobacco are particular for their intended use. One form of tobacco is known as fine cut tobacco and this is typically used for self-assembly smoking articles, such as roll-your-own smoking articles or make-your-own smoking articles.

Tobacco for self-assembly smoking articles typically has a higher moisture content than that of the tobacco material in pre-manufactured cigarettes.

As tobacco is an organic material, it can be subject to deterioration by microorganisms, such as mould. In moderate climates, mould spores are naturally present in the environment and the mould growth is favoured by moisture. Mould growth is therefore of particular concern for tobacco products having a high moisture content, such as fine cut tobacco used for self-assembly smoking articles.

Conventionally, in order to reduce or inhibit mould growth in tobacco for self-assembly smoking articles, one or more preservatives and/or humectants have been included in the tobacco. However, the use of preservatives or humectants in tobacco products may not be desirable for various reasons. For example, they may provide adverse flavour or burning properties for the fine cut tobacco.

WO 2009/056609, US 2009/025738 and WO 2009/056611 each describe methods for heating smokeless products not suitable for combustion, which contain ground particles of tobacco, such that they become pasteurised.

In earlier Philip Morris Products S.A patent application WO 2013/127528A1 it was proposed to pasteurise fine cut tobacco having a cut width of between 0.5 mm and 0.9 mm, in order to avoid or reduce the reliance on using preservatives and/or humectants in the tobacco.

However, the inventors of the present invention have identified that certain types of fine cut tobacco will have particular properties that could be expected to make such general pasteurisation ineffective in reducing or preventing mould growth.

For example, the inventors have appreciated that if the cut width of the fine cut tobacco is reduced to a cut width below 0.5 mm then the overall surface area of the tobacco will increase, thereby making more surface area available for mould growth. Alternatively or additionally, certain types of tobacco, such as flue cured tobacco, contain a particular level of sugar, which, under moist conditions, can promote mould growth in the tobacco.

It would therefore be desirable to provide an improved method for the pasteurisation of fine cut tobacco that would sufficiently reduce the chances of mould growth in certain types of fine cut tobacco that are particularly susceptible to mould growth.

According to a first aspect of the invention there is provided a method of making a product containing pasteurised fine cut tobacco, the method comprising arranging fine cut tobacco having a cut width of less than 0.5 mm and a moisture content of at least 18 percent by weight, and heating the fine cut tobacco such that the tobacco is pasteurised.

According to a second aspect of the invention there is provided a product containing pasteurised fine cut tobacco, the product comprising a closed package; and pasteurised fine cut tobacco within the closed container, the pasteurised fine cut tobacco having a cut width of less than 0.5 mm and a moisture content of at least 18 percent by weight, and a colony forming unit (CFU) value of less than 2 logo colony forming units per gram.

When manufacturing fine cut tobacco for self-assembly smoking articles, tobacco leaves are typically fed to a cutter with the leaves oriented such that their outer surfaces are transverse to the direction of cut. This means that the cut is made through the structure of the leaf, and therefore exposes the internal cell structure of the leaf as a surface of the fine cut strip of tobacco. These cut internal structures are rough and jagged compared to the smooth leaf surface. This provides additional microstructure on a surface of the fine cut strip of tobacco, which has the effect of increasing the surface area available to capture mould spores from the environment, and also increases the likelihood of mould spores developing within the fine cracks in the structure. Accordingly, the inventors of the present invention have appreciated that tobacco having a cut width of less than 0.5 mm will have an increased amount of exposed microstructure compared to fine cut tobacco having higher cut widths, such as 0.5 mm to 0.9 mm. The inventors of the present invention have further appreciated that this increased amount of exposed microstructure has several consequences for pasteurisation.

Firstly, the exposed microstructure provides more surface area per gram of tobacco than the smooth and waxy outer leaf surface. There is therefore more surface area for mould to grow on for tobacco having a cut width of less than 0.5 mm compared to prior art fine cut tobacco having higher cut widths, such as 0.5 mm to 0.9 mm.

Secondly, the exposed microstructure is less effective at retaining water than the non-cut outer leaf surface of the tobacco. Therefore, if the amount of exposed microstructure is increased by having a cut width of less than 0.5 mm, then the fine cut tobacco will tend to be less effective at retaining internal water. This can cause the tobacco to have a higher water activity level and therefore be more susceptible to mould growth.

Thirdly, internal sugars are more readily available from the exposed microstructure than from the smooth and waxy leaf surface. Under certain conditions, sugars can act as nutrient source for mould, and therefore the increased amount of exposed sugar created by having cut widths of less than 0.5 mm can also promote mould growth.

Although the above consequences could be expected to suggest that pasteurisation of tobacco having a cut width of less than 0.5 mm would be ineffective in sufficiently reducing the chances mould growth, the inventors of the present invention have found that, under certain conditions, it is possible to pasteurise such tobacco in a manner that will not adversely affect its flavour, whilst still remaining substantially mould free for a sustained period of time, such as at least 6 months.

In particular, as shown in Table 1 and Table 2 below, the inventors of the present invention have found that by heating the tobacco under certain conditions, a product containing pasteurised fine cut tobacco having a cut width of less than 0.5 mm can be produced, without adversely affect its flavour, whilst also remain substantially mould free for a sustained period of time, such as at least 6 months. The present inventors have therefore successfully produced a product containing pasteurised fine cut tobacco, where the product comprises a closed container with pasteurised fine cut tobacco within the closed container, and the pasteurised fine cut tobacco has a cut width of less than 0.5 mm and a colony forming unit (CFU) value of less than 2 log_(io) colony forming units per gram. The inventors have also found that the pasteurised fine cut tobacco of the invention can have a colony forming unit (CFU) value of less than 2 log_(io) colony forming units per gram, up to 6 months after the tobacco has been pasteurised.

Without wishing to be bound by theory, the inventors believe that this can be achieved by ensuring that the fine cut tobacco has a moisture content of at least 18 percent by weight. In particular, the inventors have identified that the combination of a cut width of below 0.5 mm and a moisture content of above 18 percent permits the strands of fine cut tobacco to reside more closely to one another, and thereby lower the filling power of the tobacco. This means that less gas will tend to be trapped amongst the tobacco strands during pasteurisation, thereby creating less of an insulating effect. This can have several advantageous effects. For example, it can reduce the time that it takes for the tobacco to reach the intended pasteurisation temperature, and therefore can improve the efficiency of the treatment process. More tobacco could therefore be pasteurised within a given time frame. Alternatively or additionally, more time can be available for maintaining the tobacco at the intended pasteurisation temperature, if desired. Reducing the amount of gas trapped amongst the tobacco strands can also reduce the chances of hot or cold spots forming amongst the fine cut tobacco.

Preferably, the fine cut tobacco has a filling power of less than 5 cubic centimetres/g, more preferably less than 4 cubic centimetres/g. The filling power of fine cut tobacco is normally expressed as “Cylinder Volume (CV)”. As is known in the art, to determine the Cylinder Volume of fine cut tobacco, a sample of fine cut tobacco should be placed in a cylindrical container and subjected to a set load for a set duration. This test is performed using a known DD60 Densimeter device (manufactured and made commercially available by Heinr. Borgwaldt GmbH, Germany). The device is fitted with a measuring head for fine cut tobacco and a cylindrical tobacco container. The tobacco is placed within the tobacco container and the measuring head is brought into contact with the tobacco sample. The measuring head then subjects the tobacco to a load of 2 kg for a duration of 30 seconds. The height (h) of the tobacco sample after the loading time is measured. The cylinder volume is then calculated using the following formula:

${C\; V} = \frac{r^{2} \cdot h \cdot \pi}{S\; {W \cdot 10}}$

Where:

“CV” is the cylinder volume in cubic centimetre/g, “r” is the radius of the cylinder container, “h” is the height in millimetres of the sample in the container after the load has been applied for 30 seconds, “SW” is the weight of the tobacco sample, and “10” is a factor for converting “h” from millimetres to centimetres.

Preferably during the heating step, the fine cut tobacco is heated to a pasteurisation temperature of at least 75 degrees Celsius, even more preferably at least 80 degrees Celsius.

Preferably, during the heating step, the fine cut tobacco is heated to a pasteurisation temperature of less than 95 degrees Celsius, even more preferably less than 90 degrees Celsius. In preferred embodiments, during the heating step, the fine cut tobacco is heated to a pasteurisation temperature of between 75 and 95 degrees Celsius, more preferably between 80 and 90 degrees Celsius. In some preferred embodiments, during the heating step, the fine cut tobacco is heated to a pasteurisation temperature of about 85 degrees Celsius. Below such temperatures, it has been identified that the tobacco may not be effectively pasteurised for it to remain substantially mould free for a sustained period of time, such as at least 6 months. Above such temperatures, it is believed that the flavour of the tobacco can be adversely affected by the heating.

Preferably, during the heating step, the tobacco is heated such that it remains substantially at a pasteurisation temperature for a duration of at least 3 minutes, more preferably at least 4 minutes. Preferably, during the heating step, the tobacco is heated such that it remains substantially at a pasteurisation temperature for a duration of less than 7 minutes, more preferably less than 6 minutes. In some preferred embodiments, during the heating step, the tobacco is heated such that it remains substantially at a pasteurisation temperature for a duration of between 3 minutes and 7 minutes, more preferably between 4 minutes and 6 minutes, and even more preferably for about 5 minutes.

Preferably, the fine cut tobacco has a water activity level of at least 0.7 Aw after pasteurisation. Preferably, the fine cut tobacco has a water activity level of less than 0.8 Aw after pasteurisation. Such relatively high water activity levels, can advantageously allow the fine cut tobacco to be sufficiently flexible to facilitate manufacture, and handling by a consumer, and in particular, the self-assembly of a smoking article containing the fine cut tobacco. The high water activity level is particularly beneficial for the present invention where the cut width is less than 0.5 mm as the strands of tobacco are more delicate and brittle at this cut width.

Preferably, the fine cut tobacco is free from preservatives. Possible preservatives used in tobacco products may comprise benzoic acid, sodium propionate, natamycin, non-anoic acid and salts thereof.

Additives may be added to the tobacco during manufacturing, such as sugar, cocoa, coconut powder. Humectants like for example, glycerin, propylene glycol and invert sugar and others may also be added. However, in preferred embodiments, the fine cut tobacco is free from humectants.

Preferably, the fine cut tobacco comprises at least 5 percent by dry weight of reducing sugars, more preferably at least 15 percent by dry weight of reducing sugars. Preferably, the fine cut tobacco comprises less than 25 percent by dry weight of reducing sugars, more preferably less than 23 percent by dry weight of reducing sugars. The term “dry weight” is used herein to refer to the weight of the fine cut tobacco after all moisture has been removed from the fine cut tobacco.

Flue cured tobacco typically has a higher sugar content than other types of tobacco, such as burley tobacco. Preferably, the fine cut tobacco comprises at least 40 percent by weight of flue cured fine cut tobacco, more preferably at least 60 percent by weight of flue cured fine cut tobacco. Preferably, the fine cut tobacco comprises less than 80 percent by weight of flue cured fine cut tobacco.

As noted above, the present invention applies to fine cut tobacco having a cut width of less than 0.5 mm. The fine cut tobacco comprises elongate strips or strands of tobacco that have been cut at a predetermined width. The length of the strips typically range from 2 cm to 10 cm. Preferably, the fine cut tobacco has a cut width of at least 0.1 mm, even more preferably at least 0.2 mm. Preferably the fine cut tobacco has a cut width of less than 0.4 mm. In some preferred embodiments, the fine cut tobacco has a cut width of between 0.1 mm and 0.4 mm, or between 0.2 mm and 0.4 mm. The fine cut tobacco is intended for use in combustible smoking articles, for example self-assembly smoking articles, such as roll-your-own or make-your own smoking articles.

As noted above, the present invention applies to fine cut tobacco having a moisture content of at least 18 percent by weight. Preferably, the moisture content of the tobacco is at least 20 percent by weight, more preferably at least 22 percent by weight. Preferably, the moisture content of the tobacco is less than 27 percent by weight, more preferably less than 25 percent by weight. In some particularly preferred embodiments, the moisture content of the tobacco is between 18 and 25 percent by weight, more preferably between 20 and 25 percent by weight and even more preferably between 20 and 23 percent by weight. It is thought that such preferred moisture content ranges advantageously allow the fine cut tobacco to be sufficiently moist for rolling and handling purposes, without being too moist for combustion or too moist for pasteurisation to be effective in sufficiently preventing or inhibiting mould growth. It is also thought that this permits the strands of fine cut tobacco to reside more closely to one another, and thereby lower the filling power of the tobacco The desired tobacco moisture content is typically set during tobacco processing comprising the addition of water and drying.

The cut width is particularly important for fine cut tobacco that can be used for self-assembly smoking articles, such as roll-your-own or make-your-own smoking articles, which requires elongate strips or strands of fine cut tobacco in a certain size in order to prevent the tobacco from falling out at the open end of the smoking article. In contrast to the present invention, for chewing tobacco, and snus, the tobacco is mostly ground or sometimes finely cut. However, this typically results into a sort of dust that then creates the typical snus pulp filled in the sachets for oral consumption. Similarly, snuff is provided as a ground or finely cut powder.

Preferably, the closed package used in the present invention is a retail package and suitable for product distribution and sale. As the method according to the invention eliminates the need for further processing or handling the tobacco after the pasteurization step, the tobacco is well protected from environmental factors which could adversely impact the quality of the tobacco before use, for example, the ingress of microorganisms. Preferably, the closed package is substantially air-tight before use. Preferably, the moisture content of the fine cut tobacco remains substantially constant between packaging and use.

Preferably, the closed package is a pouch comprising a pocket that contains the fine cut tobacco and a flap configured to fold over the pocket. Alternatively, the closed package is preferably a stand up bag formed of flexible material, and the bag comprises a base and at least two side walls. Alternatively, the closed package is preferably a rigid tin or container. Preferably, the closed package is designed to withstand the pasteurisation conditions of the present invention, so that the fine cut tobacco can be pasteurised within the closed package if desired. Preferably at least part of the closed package is made of a laminate which provides a moisture barrier and is impermeable to microorganisms. Further, the closed package is preferably permeable to microwaves. Preferably, the fine cut tobacco is sealed in the closed package.

Preferably, the packaging material is plastic, metal, metalized or cardboard laminates or a combination thereof. Preferably, the closed package is made of a laminate wherein at least one layer provides a moisture barrier. In other the embodiments, the closed package may provide a moisture barrier, without being made from a laminate material. This allows, that in particular during the heating, no moisture will escape the closed package, such that the moisture content in the tobacco will remain constant. Same benefit is also provided during the latter transport and while the closed package is kept on a shelf for storage and sale, as no evaporation of moisture from the fine cut tobacco to the outside of the closed package can occur.

The closed package is preferably suitable for product sale to the consumer. Preferably the closed package has a weight of 5 g to 500 g. This is a common range for retail tobacco packages. In particular, pouches with around 10 g up to 100 g and closed boxes with around 50 g up to 150 g of tobacco may be provided as the closed package according to the invention.

The packaged fine-cut tobacco according to the invention may be used for self-assembly smoking articles, such as make-your-own or roll-your-own products, wherein it has been pasteurized to provide enhanced shelf-life and improved sensory properties.

Preferably, the heating is carried out by subjecting the fine cut tobacco to a heating medium. The heating medium may be water, steam, air, an inert gas, or any combination thereof. The heating medium may be a mixture of water micro-droplets and saturated steam. Alternatively, the heating medium may be a mixture of water, superheated steam and air. Further, the heating medium may be a mixture of water, steam and air.

Advantageously, a package according to the invention may be further overwrapped by a water proof outer wrapper to prevent damage to the package that could be otherwise caused by the heating medium, such as water. This is particularly advantageous where the package comprises print or cardboard or both.

In some preferred embodiments, the fine cut tobacco is heated by means of radiation, more preferably microwave radiation. This can be particularly beneficial for the present invention because the fine cut tobacco has a high moisture content of at least 18 percent by weigh, and so the microwave radiation can more quickly heat up the fine cut tobacco. This can reduce the amount of time required for the tobacco to reach a pasteurisation temperature.

If the tobacco is pasteurised by microwave power, then the microwave power applied to the tobacco packages may be controlled based on the temperature measured at the centre of the packages, for example by means of an infrared temperature sensor, such as an infrared camera. The position of the fine cut tobacco may be controlled during pasteurization relative to the position of the microwave heating apertures.

The pressure during pasteurization is preferably controlled in dependency of the temperature of the treatment and the heating medium outside the package or pasteurization medium inside the package used.

Preferably, the temperature of the tobacco is monitored during the heating step. This can be obtained by monitoring the temperature around the fine cut tobacco, and estimating from this temperature the temperature of the tobacco. Furthermore, the temperature of the tobacco may be measured by infrared sensors. The monitoring of the temperature allows as well controlling of the temperature during the heating step.

After the heating step, a cooling step may be carried out by subjecting the fine cut tobacco to a cooling medium, such as cold air, water or inert gas. Gaseous cooling or heating media are preferred over liquid heating media.

If the fine cut tobacco is subjected to pasteurisation conditions when in the closed package, preferably, the temperature in the centre of the closed package, which is suitable for product sale to the consumer, is measured at the start and at the end of a heating step, and the applied heating power for a subsequent heating step is adjusted to achieve a uniform, desired temperature of the tobacco throughout the closed package. The temperature may also be controlled or monitored during the cooling step, if this step is present.

It shall be appreciated that any features described with reference to one aspect of the present invention are equally applicable to any other aspect of the invention.

Preferred embodiments of the invention in its various aspects will now be described by way of non-limiting example with reference to the attached figures, in which

FIG. 1 shows an exemplary manufacturing line for the method according to the invention; and

FIG. 2 shows a Graph representing plots of mould levels over a 6 month storage period.

The present invention relates to a method for pasteurization of tobacco, in particular fine-cut tobacco for roll-your-own and make-your-own products.

Generally, in the first stage tobacco leaves or tobacco leaf pieces will be processed in a common manner, including conditioning, sorting and separation of unwanted material. Then, the leaves or leaf pieces are cut into fine cut tobacco with a cut width of less than 0.5 mm, and water and additional ingredients such as additives are optionally added. Finally, the tobacco is dried to a certain moisture content, in particular more than 18 weight percent.

The accordingly processed tobacco is indicated with reference number 1 in FIG. 1.

In accordance with this embodiment, the tobacco 1 is then filled in a package 2 in a packing station 3. However, the tobacco may instead be pasteurised in bulk, for example by conveying unpackaged tobacco through a heating station for pasteurisation, and then subsequently packaging the tobacco after the heating station.

As shown in FIG. 1, the packing station 3 further provides that the package 2 is closed, such that it is hermetically sealed. In particular, the package 2 is a flexible pouch, which will be heat sealed to be closed. However, the closure of the package 2 can be designed such that is openable by a consumer, without the pouch being destroyed. In particular the package 2 is adapted to be reclosable. Alternatively or additionally to closing the package by heat sealing, the package 2 may be provided with adhesive to be closed such that it is hermetically sealed. In some embodiments the package 2 may be heat sealed on some of the sides, while a reclosable opening is only provided with adhesive. The adhesive provided on the opening of the package 2 is in particular non-permanent adhesive allowing as well to reclose the package substantially airtight.

From the packing station 3, the closed packages 2 are transported by a conveyance means 4, for example a conveyance belt, to the heating station 5. In the heating station 5 the packages 2 are heated such that the tobacco 1 therein is pasteurized. In particular, the packages 2 will be heated until the fine cut tobacco reaches a pasteurisation temperature of between 75 to 95 degrees Celsius. Once the packages are at such a pasteurisation temperature, the packages are then subjected to this temperature for a duration of 2 to 7 minutes. Sensors may be provided for determining when the packages are at the pasteurisation temperature. The heating is carried out by using a heat medium, which in the present embodiment is hot air. The heating station 5 may be an oven with a hot air fan. A conveyance means extends through the heating station 5. The air may be filter or purified before the pasteurised tobacco is subjected to it as a heating medium.

It is important that the tobacco 1 in the core of the package 2 reaches the required target temperature, such that all tobacco 1 in the package 2 is pasteurized. As the package 2 is sealed and is made of moisture proof material, the moisture in the tobacco cannot escape the package 2, and is, thus, held at a constant level.

During the heating step, the temperature of the tobacco 1 is preferably monitored, either directly or indirectly by monitoring the temperature of the package 2. The heat that needs to be applied will depend on the type and size of the package 2, while the temperature of the tobacco 1 is used as an indication of the pasteurization process.

Thus, the presence of microorganisms such as mould is reduced in the tobacco 1, so that the tobacco 1 in the packages 2 can have a longer shelf life.

After the heating in the heating station 5, the closed packages 2 are further transported to a cooling station 6, in which a cooling step is carried out. A conveyance means extends through the cooling station 6. For the cooling step, ambient or cold air is used, to cool the product down to ambient temperature or to a temperature below ambient temperature. In particular, the package 2 is cooled down to 2 to 10 degrees Celsius, and is subsequently kept at this temperature during further transport until it reaches the point of sale such that the shelf life is increased.

Typical shelf life for tobacco treated with the aforementioned method is at least 6 months.

Various studies were performed to determine the effect of different pasteurisation conditions on different samples of fine cut tobacco. Results from these studies are shown in Table 1, Table 2 and FIG. 2.

Table 1 shows the cut width, moisture content and added humectant values for five different samples of fine cut tobacco that were subjected to pasteurisation trials. In order to assess the effectiveness of the pasteurisation across a range of initial mould levels, each sample was divided into two sub-categories; inoculated and non-inoculated. The inoculated samples were ones for which the tobacco sample was first inoculated with mould, by a dry rubbing technique where the tobacco was rubbed on the surface of agar plates containing cultured moulds of P. chrysogenum and A. (Eurotium) amstelodami. In order to achieve a desired level of 10⁶-10⁷ colony forming units/gram 200 mould containing DG-18 plates were used, with approximately 20 grams of tobacco being rubbed on each plate. The rubbed tobacco was then placed into a large bag and shaken to ensure even mixing of the tobacco prior to filling individual pouches of tobacco.

Each inoculated and non-inoculated sample was then divided into 3 further subcategories for different pasteurisation conditions. These were pasteurisation at 70 degrees Celsius for 5 minutes, pasteurisation at 75 degrees Celsius for 5 minutes and pasteurisation at 85 degrees Celsius for 5 minutes. The reduction in mould level for each category is shown in Table 1 below. The shaded cells indicate the samples for which the mould level was reduced below the limit of detection (approximately <0.5 log colony forming units per gram).

TABLE 1 Sample Overview and Mould Level Reduction Reduction In Mould Levels (log₁₀cfu/g) After 5 Tobacco Sample Minutes Treatment at 70, 75 or 85° C. Cut Moisture Added 70° C. 75° C. 85° C. Sample Width Content Humectant Non- Non- Non- No. (mm) (% weight) (% weight) Inoculated Inoculated Inoculated Inoculated Inoculated Inoculated 1 0.3 21.9 5 4.85 0.37 6.32 2.16 6.67 2.04 2 ≥0.5 22.2 5 3.04 0 6.51 2.91 6.47 2.17 3 0.4 21.7 5 5.36 1.33 6.47 2.57 6.95 2.28 4 0.4 22.9 5 5.55 2.77 5.61 2.68 6.67 3.2 5 ≥0.5 21.4 5 2.93 0.25 6.81 2.26 6.85 2.37 6 0.3 23 5 4.11 1.21 6.51 1.8 6.58 1.8 7 0.3 23 0 4.99 1.69 4.84 2.17 6.77 2.66

Therefore, as can be seen in Table 1, the mould level in all samples with cut widths of greater than or equal to 0.5 mm could be reduced below the limit of detection through pasteurisation at temperatures of 75 degrees Celsius or more. The mould level in samples 3 and 6 (i.e. ones having a cut width of less than 0.5 mm) could also be reduced below the limit of detection through pasteurisation at temperatures of 75 degrees Celsius or more. However, a pasteurisation temperature of greater than 75 degrees Celsius was needed to reduce the mould level in samples 1, 4 and 7 below the limit of detection.

A shelf life study of the pasteurised samples was then conducted. In particular, after the samples had been subjected to the pasteurisation conditions set out in Table 1, they were then stored at 25 degrees Celsius for a period of at least 6 months and the mould level in each sample was measured at set points throughout the 6 month period. The measured mould level for each inoculated sample is shown in Table 2 below.

TABLE 2 Shelf Life Analysis of Each Sample Mould Levels (log₁₀cfu/g) Of Inoculated Samples Throughout 6M Tobacco Sample At Storage At 25° C., After Heating For 5 minutes At 70, 75 or 85° C. Different Temperature 0.1 Month 1 Month 2 Months 4 Months 6 Months 1 (0.3 mm) 70° C. 2.32 3.01 2.23 ≤1.82 ≤1.4 75° C. ≤0.85 <0.5 <0.5 <0.5 ≤1.08 85° C. <0.5 <0.5 <0.5 <0.5 ≤1.45 2 (0.5 mm) 70° C. 4.33 3.86 3.80 ≤3.3 ≤1.75 75° C. <0.5 <0.5 <0.5 <0.5 ≤0.5 85° C. <0.5 <0.5 <0.5 <0.5 <0.5 3 (0.4 mm) 70° C. 2.14 0.90 ≤0.91 2.71 ≤0.57 75° C. <0.5 <0.5 <0.5 <0.5 <0.5 85° C. <0.5 <0.5 <0.5 <0.5 <0.5 4 (0.4 mm) 70° C. 1.66 3.57 ≤2.1 0.5 ≤1.15 75° C. ≤1.49 <0.5 ≤1.2 <0.5 ≤0.69 85° C. <0.5 <0.5 <0.5 <0.5 <0.5 5 (0.5 mm) 70° C. 4.12 3.97 ≤2.5 3.54 3.33 75° C. <0.5 ≤1.46 ≤1.12 3.8 ≤2.14 85° C. <0.5 <0.5 <0.5 3.91 2.8 6 (0.3 mm) 70° C. 2.74 1.15 ≤1.72 2.24 2.15 75° C. <0.5 <0.5 <0.5 <0.5 2.47 85° C. <0.5 <0.5 <0.5 <0.5 1.97 7 (0.3 mm) 70° C. 2.18 5.16 2.52 mouldy mouldy 75° C. 2.33 5.78 4.42 mouldy mouldy 85° C. <0.5 1.6 <0.5 <0.5 <0.5

As can be seen from Table 2, for all samples there were surviving moulds throughout the 6 month shelf life, if the tobacco had been subjected to a pasteurisation temperature of 70 degrees Celsius for 5 minutes. For all samples (except sample 7) there were very low levels or non-detectable levels of moulds throughout the 6 month shelf life, if the tobacco had been subjected to a pasteurisation temperature of 75 degrees Celsius or more for 5 minutes.

Interestingly, sample 7 behaved differently from the other samples. In particular, the inoculated and non-inoculated categories of sample 7 that were heated for 5 minutes at 70 degrees Celsius or 75 degrees Celsius went mouldy between 2 and 4 months of storage. However, when sample 7 was heated at 85 degrees Celsius for 5 minutes, both its inoculated and non-inoculated versions remained mould free for the full duration of the 6 months storage. Sample 7 was the only sample that did not contain added humectant, meaning it was likely to contain more free water on its surface. Wth a moisture content of at least 18 percent weight (in this case 23 percent by weight), this would be expected to significantly promote mould growth, so it is particularly surprising that pasteurisation at a temperature of 85 degrees Celsius for 5 minutes was sufficient to prevent detectable mould growth on the inoculated version of sample for a duration of at least 6 months. This can be best appreciated from FIG. 2. 

1. A method of making a product containing pasteurised fine cut tobacco for combustible use, the method comprising: arranging fine cut tobacco comprising elongate strips of tobacco having a cut width of less than 0.5 mm and a moisture content of at least 18 percent by weight, and heating the fine cut tobacco such that the tobacco is pasteurised.
 2. A method according to claim 1, wherein the fine cut tobacco has a moisture content of between 20 and 25 percent by weight.
 3. A method according to claim 12, wherein the fine cut tobacco has a moisture content of between 20 and 23 percent by weight.
 4. A method according to claim 1, wherein the fine cut tobacco has a water activity level of between 0.7 Aw and 0.8 Aw after the fine cut tobacco has been pasteurised.
 5. A method according to claim 1, wherein during the heating step, the fine cut tobacco is heated to a pasteurisation temperature of between 75 and 95 degrees Celsius.
 6. A method according to claim 5, wherein during the heating step, the fine cut tobacco is heated to a pasteurisation temperature of between 80 and 90 degrees Celsius.
 7. A method according to claim 1, wherein the heating step is carried out such that the fine cut tobacco is heated at a pasteurisation temperature for a duration of between 3 and 7 minutes.
 8. A method according to claim 1, wherein the fine cut tobacco comprises between 5 and 25 percent by dry weight of reducing sugars.
 9. A method according to claim 1, wherein the arranging step further comprises arranging the fine cut tobacco in a package, and the heating step further comprises heating the fine cut tobacco in the package.
 10. A method according to claim 1, wherein the fine cut tobacco has a cut width of between 0.2 mm and 0.4 mm.
 11. A method according to claim 1, wherein the fine cut tobacco has a filling power of less than 5 cubic centimetres/g.
 12. A product containing pasteurised fine cut tobacco for combustible use, the product comprising: a closed package; and pasteurised fine cut tobacco comprising elongate strips of tobacco within the closed package, the pasteurised fine cut tobacco having a cut width of less than 0.5 mm and a moisture content of at least 18 percent by weight, and a colony forming unit (CFU) value of less than 2 logio colony forming units per gram.
 13. A product according to claim 12, wherein the fine cut tobacco has a water activity level of between 0.7 Aw and 0.8 Aw.
 14. A product according to claim 12, wherein the fine cut tobacco comprises between 5 and 25 percent by dry weight of reducing sugars.
 15. A product according to claim 10, wherein the pasteurised fine cut tobacco is sealed in the closed package.
 16. A product according to claim 10, wherein the closed package is a pouch comprising a pocket that contains the fine cut tobacco and a flap configured to fold over the pocket, or wherein the closed package is a stand up bag formed of flexible material, and the bag comprises a base and at least two side walls, or wherein the closed package is rigid tin or container. 